[英]Constantly getting undefined when iterating through an array
So I'm just practising my react redux skills. 所以我只是练习我的反应减速技能。 Im a beginner. 我是初学者。 I have created an action, reducer and several components. 我创建了一个动作,减速器和几个组件。 I'm basically making a todo app. 我基本上是在做一个todo应用程序。 I am fetching the data from an API which I have successfully done but the problem is arising when I'm trying to loop through the data and have it surrounded with <li>
tags. 我正在从我已成功完成的API中获取数据,但是当我尝试循环数据并将其包含在<li>
标记中时,问题就出现了。 I am getting Cannot read property 'map' of undefined
which i dont understand why because in the console i can clearly see the array. 我得到了Cannot read property 'map' of undefined
,我不明白为什么,因为在控制台中我可以清楚地看到数组。
Action: 行动:
export function getLists(){
return function (dispatch) {
return fetch ("https://reqres.in/api/users?page=1")
.then( response => response.json())
.then (json => {console.log('sdsd'); console.log(json);
dispatch({ type: "ADD_ITEMS", payload: { json, loading: false} });
});
}
}
Reducer: 减速器:
const initialState = {
todothings: [],
loading: true
};
function rootReducer (state = initialState, action) {
if( action.type === "ADD_ITEMS"){
console.dir("In the ADD_ITEMS reducer" + action.payload);
return Object.assign({}, state, {
todothings: state.todothings.concat(action.payload.json),
loading: action.payload.loading,
});
} else if ( action.type === "DELETE_ITEM") {
} else {
return state;
}
}
export default rootReducer;
ToDo Components: 待办事项组件:
import React, { Component } from 'react';
import { getLists } from '../actions/index';
import { connect } from 'react-redux';
import TodoItems from './TodoItems';
class TodosComponent extends Component {
componentDidMount(){
console.log('in the Todos comp -> componentDidMount()');
this.props.getList();
}
render(){
const {todothings , loading} = this.props;
if(!loading){
return(
<div>
<p>dfd</p>
{console.log(todothings)}
<TodoItems list={todothings}></TodoItems>
</div>
)
} else {
return (
<p>Fetching from upstream.</p>
)
}
}
}
function mapStateToProps(state){
return {
todothings: state.todothings,
loading: state.loading,
}
}
function mapDispatchToProps(dispatch){
return {
getList: () => dispatch(getLists())
};
}
const Todos = connect(mapStateToProps, mapDispatchToProps)(TodosComponent)
export default Todos;
TodoItem Component: TodoItem组件:
import React from 'react';
function TodoItems (props) {
return(
<div>
<ul>
{console.log('In the todoitems')}
{console.log(props)}
{props.list.map( element => (
<p>{element.data}</p>
))}
</ul>
</div>
);
}
export default TodoItems;
EDIT: 编辑:
This is what I have so far now: 这就是我现在所拥有的:
ToDoItems: ToDoItems:
import React from 'react';
const TodoItems = ({ list = [] }) => {
if (list.length === 0) return null;
return (
<ul>
{list.map(item => (
<li key={item.id} {...item}>
<p>{item.first_name}</p>
</li>
))}
</ul>
);
};
export default TodoItems;
ToDo Component: ToDo组件:
import React, { Component } from 'react';
import { getLists } from '../actions/index';
import { connect } from 'react-redux';
import TodoItems from './TodoItems';
class TodosComponent extends Component {
componentDidMount(){
console.log('in the Todos comp -> componentDidMount()');
this.props.getList();
}
render(){
const {todothings , loading} = this.props;
if(!loading){
return(
<div>
<p>dfd</p>
{console.log('in the todo comp')}
{console.log(todothings)}
<TodoItems list={todothings.data}></TodoItems>
</div>
)
} else {
return (
<p>Fetching from upstream.</p>
)
}
}
}
function mapStateToProps(state){
return {
todothings: state.todothings,
loading: state.loading,
}
}
function mapDispatchToProps(dispatch){
return {
getList: () => dispatch(getLists())
};
}
const Todos = connect(mapStateToProps, mapDispatchToProps)(TodosComponent)
export default Todos;
Reducer: 减速器:
const initialState = {
todothings: [],
loading: true
};
function rootReducer (state = initialState, action) {
if( action.type === "ADD_ITEMS"){
console.dir("In the ADD_ITEMS reducer" + action.payload);
return Object.assign({}, state, {
todothings: state.todothings.concat(action.payload.json.data),
loading: action.payload.loading,
});
} else if ( action.type === "DELETE_ITEM") {
} else {
return state;
}
}
export default rootReducer;
Action: 行动:
export function getLists(){
return function (dispatch) {
return fetch ("https://reqres.in/api/users?page=1")
.then( response => response.json())
.then (json => {console.log('sdsd'); console.log(json);
dispatch({ type: "ADD_ITEMS", payload: { json, loading: false}
});
});
}
}
There are now no errors yet nothing is getting displayed: 现在没有错误,但没有显示任何内容:
(3) [{…}, {…}, {…}]
0: {id: 1, email: "george.bluth@reqres.in", first_name: "George", last_name: "Bluth", avatar: "https://s3.amazonaws.com/uifaces/faces/twitter/calebogden/128.jpg"}
1: {id: 2, email: "janet.weaver@reqres.in", first_name: "Janet", last_name: "Weaver", avatar: "https://s3.amazonaws.com/uifaces/faces/twitter/josephstein/128.jpg"}
2: {id: 3, email: "emma.wong@reqres.in", first_name: "Emma", last_name: "Wong", avatar: "https://s3.amazonaws.com/uifaces/faces/twitter/olegpogodaev/128.jpg"}
length: 3
__proto__: Array(0)
Afternoon, 下午,
I think the data you want is from prop.list.data
not props.list
within <TodoItems />
我想你想要的数据是来自prop.list.data
不props.list
内<TodoItems />
In your component <TodDo />
try: 在您的组件<TodDo />
尝试:
<TodoItems list={todothings.data}></TodoItems>
Then tidy up your stateless component <TodoItems />
(to cover an empty array): 然后整理你的无状态组件<TodoItems />
(以覆盖一个空数组):
const TodoItems = ({ list = [] }) => {
if (list.length === 0) return null;
return (
<ul>
{list.map(item => (
<li key={item.id} {...item}>
<ul>
{Object.keys(item).map((data, key) => (
<li {...{ key }}>{data}</li>
))}
</ul>
</li>
))}
</ul>
);
};
Note: 注意:
Your array has an object, with this shape: 您的数组有一个对象,具有以下形状:
{
id: 1,
email: "g.buth@reqres.in",
first_name: "George",
last_name: "Bluth"
}
What do you want to return in your <li>
? 你想在<li>
回报什么?
Update to loop through object. 更新循环对象。
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